1. Field of the Invention
This invention relates to an electrophotographic recording apparatus such as an LED printer having an exposing device for exposing a photosensitive member to light emitted from a light emitting device such as a light emitting diode (LED) according to image data.
2. Description of the Related Art
An electrophotographic recording apparatus such as an LED printer effects the exposing operation of forming an electrostatic latent image corresponding to image data on a photosensitive member by selectively setting a large number of light emitting diodes constituting an LED array into the activated and non-activated states and exposing the photosensitive member to light emitted from the activated light emitting diodes.
In the electrophotographic recording system, after the above exposing operation, the developing, transfer and fixing operations are effected. At this time, if each of black pixels constituting an electrostatic latent image created on the photosensitive member by the exposing operation has a diameter A, for example, toners are attached to the electrostatic latent image in a larger area than the electrostatic latent image in the developing operation. That is, the diameter of a toner image for one pixel becomes B which is larger than A. The toner image is further extended i the following transfer operation and fixing operation.
Thus, the size of the pixel recorded on the paper sheet becomes relatively larger than that of the pixel of the electrostatic latent image. As a result, the peripheral portions of toner images of adjacent pixels are overlapped with each other to provide a solid black image of high black concentration (for example, not less than 1.0 O.D.). However, in a case where a picture image is recorded by use of the artificial half tone such as dither, that is, when the half tone is created by selectively removing the black pixels, the toner will extend out of one pixel area so that preferable gradation cannot be attained. Further, when small characters are recorded, the recorded characters may be crushed.
Therefore, it is considered to reduce the size of the pixel of the electrostatic latent image and set the toner image of one pixel within the pixel area by reducing an amount of emitted light of the light emitting diode or reducing the period of light emitting time. In this case, preferable half tone can be attained, but when the solid black picture image is recorded, gaps are made between the pixels, thus making it impossible to attain sufficiently high solid black concentration.
As described above, in the prior art, it is difficult to record both the picture images such as characters and images of artificial half tone (such as dither) created by dispersedly arranged pixels and the picture images such as solid black picture images created by densely arranged pixels in good conditions.